The present application relates generally to variable speed drives. The application relates more specifically to an integral bypass contactor for a variable speed drive incorporating an active converter.
A variable speed drive (VSD) for heating, ventilation, air-conditioning and refrigeration (HVAC&R) applications typically includes a rectifier or converter, a DC link, and an inverter.
Typical VSD bypasses are active only when the VSD is incapable of running, e.g., in emergency situations. The bypass incorporates a minimum of two sets of three-phase contactors, one in series with the output of the inverter section and another between the incoming mains and the motor. Bypass means may be actuated via operator intervention via the drive keypad, or may have automatic switchover to the bypass mode if the VFD fails. Transfer of the motor load from VSD operation to mains operation may result in locked rotor torque being presented to the mechanical load and very high motor inrush current as the motor is started across-the-line.
What are needed are a system and/or method that satisfy one or more of these needs or provides other advantageous features. Other features and advantages will be made apparent from the present specification. The teachings disclosed extend to those embodiments that fall within the scope of the claims, regardless of whether they accomplish one or more of the aforementioned needs.